The invention relates to a method for determining boil states of the contents of cooking utensils on range cook-tops. More specifically, the invention relates to a method for determining boil states using an acoustic sensor system.
Boiling water or other fluids or foods (generically "liquids") is one of the most common uses for a range. It is typically desirable to closely monitor the boil phase of the liquid during such processes, i.e., to identify the pre-simmer, simmer onset, simmer and/or boil phases. In this regard, the pre-simmer phase is generally characterized by a calm liquid and the simmer onset phase is the initial, slow bubbling of the liquid characterized by the appearance of individual bubbles. During the simmer phase, bubbles appear in jets creating the effect commonly referred to as simmering. Finally, in the boil phase, the bubbling of the liquid is generalized, resulting in the familiar turbulence of a boiling liquid. These phases can be identified by experts and experienced cooks. The formation and collapse of the bubbles during the phases create an acoustic signature which changes with the size and number of the bubbles, the rate of their formation, their collapse, and the temperature gradient in the liquid. This acoustic response includes the audible component, which can be easily observed when cooking, as well as responses in various frequency bands. It is also affected by factors including the type of cooking vessel and any ingredients in the liquid.
The boil phase is monitored for a number of reasons. First, many cooking processes require that the liquid be attended to upon identification of a particular boil phase, e.g., stirring or adding ingredients. In addition, the boil phase may be monitored to reduce heat after the liquid reaches a boil, either to reduce it to a simmer for cooking purposes or so as to prevent boil-over. Boil-over can result in a burned-on mess or, in the case of gas ranges, extermination of the cooking flame. Moreover, a liquid not monitored upon boiling can boil dry, resulting in burning of the food, damage to cooking utensils, or potentially a fire or other safety hazard.
Conventionally, the boil phase is monitored visually. Such visual monitoring can interfere with the user's ability to prepare other foods or be otherwise fully productively disposed during heating of the liquid. Moreover, a busy or inexperienced cook may fail to accurately and in a timely manner identify a boil phase of interest.
Increasingly, in the market for household appliances, manufacturers seek to provide, and consumers desire to have, appliances with a greater degree of automated operation and control. With the increasing affordability of integrating computing power into an appliance, there exists a potential to provide the increased levels of automated control. However, the information gathering tools or devices that will interact with a computer or processor in monitoring or controlling the operation of the appliance must also have desirable cost/performance attributes.
For cooking appliances generally, and for electric, inductive, and gas range cook-tops specifically, automation or partial automation of control of the cooking process, or monitoring of cooking on a cook-top, has traditionally focused on temperature monitoring or sensing. Various temperature sensors have been proposed for sensing the temperature of a surface heating unit or a cooking utensil positioned thereon, and for controlling the heat input to the heating unit, based upon the sensed temperature. Such sensors have commonly been proposed for use in connection with glass-ceramic radiant cook-tops. Another form of temperature based sensing is a direct food probe which is inserted into the liquid to measure temperature directly.
Temperature-based sensing systems for ranges or cook-tops may indirectly or inferentially provide information regarding a boil state of a liquid contained in a utensil and being heated on the cook-top. However it continues to be a problem in cook-top sensing and control to provide a method for reliably determining the boil state since the correlation between temperature and boil state depends on a number of variables including, but not limited to, type of liquid, the amount of liquid, any additives, the position of the utensil, and the utensil's warpage. For instance it is well known that the addition of salt into water raises the boiling temperature. Environmental conditions such as elevation can also affect the temperature associated with boil states. Finally, the position of the temperature sensor and its calibration can also have a significant impact on achievable accuracy. The general need then is to develop an approach to boil state determination that is more robust to cooking modalities, vessels used, various user interactions, and other variations or disturbances in the equipment or environment.